All crude oil contains impurities which contribute to corrosion, heat exchanger fouling, furnace coking, catalyst deactivation, and product degradation in refinery and other processes. These contaminants are broadly classified as salts, bottom sediment, and water (BS+W), solids, and metals. The amounts of these impurities vary, depending upon the particular crude. Generally, crude oil salt content ranges between about 3-200 pounds per 1,000 barrels (ptb).
Native water present in crude oils includes predominately sodium chloride with lesser amounts of magnesium chloride and calcium chloride being present. Upon thermal hydrolysis, chloride salts are the source of highly corrosive HCl, which is severely damaging to refinery tower trays and other equipment. Additionally, carbonate and sulfate salts may be present in the crude in sufficient quantities to promote crude preheat exchanger scaling.
Solids other than salts are equally harmful. For example, sand, clay, volcanic ash, drilling muds, rust, iron sulfide, metal, and scale may be present and can cause fouling, plugging, abrasion, erosion and residual product contamination. As a contributor to waste and pollution, sediment stabilizes emulsions in the form of oil-wetted solids and can carry significant quantities of oil into the waste recovery systems.
Metals in crude may be inorganic or organometallic compounds which consist of hydrocarbon combinations with arsenic, vanadium, nickel, copper, iron, and other metals. These materials promote fouling and can cause catalyst poisoning in subsequent refinery processes, such as catalytic cracking methods, and they may also contaminate finished products. The majority of the metals carry as bottoms in refinery processes. When the bottoms are fed, for example, to coker units, contamination of the end-product coke is most undesirable. For example, in the production of high grade electrodes from coke, iron contamination of the coke can lead to electrode degradation and failure in processes, such as those used in the chlor-alkali industry.
Desalting is, as the name implies, a process that is adapted (although not exclusively) to remove primarily inorganic salts from the crude prior to refining. The desalting step is provided by adding and mixing or emulsifying with the crude a few volume percentages of fresh water to contact the brine and salt. In crude oil desalting, a water in oil (W/O) emulsion is intentionally formed with the water admitted being on the order of about 3-10 volume % based on the crude oil. Water is added to the crude and mixed intimately to transfer impurities in the crude to the water phase. Separation of the phases occurs due to coalescence of the small water droplets into progressively larger droplets and eventual gravity separation of the oil and underlying water phase.
Demulsification agents are added, usually upstream from the separation vessel, and have a variety of purposes such as to help in providing maximum mixing of the oil and water phases, dehydrate the crude oil, provide faster water separation, better salt extraction or improved solids extraction and generate oil-free effluent water. Known demulsifying agents include water soluble organic salts, sulfonated glycerides, sulfonated oils, acetylated caster oils, ethoxylated phenol formaldehyde resins, polyols, polyalkylene oxides, ethoxylated amines, a variety of polyester materials, and many other commercially available compounds.
Desalters in refineries are also commonly provided with electrodes to impart an electrical field in the desalter. This serves to polarize the dispersed water molecules. The so-formed dipole molecules exert an attractive force between oppositely charged poles with the increased attractive force increasing the speed of water droplet coalescence by from ten to one hundred fold. The water droplets also move quickly in the electrical field, thus promoting random collisions that further enhance coalescence.
Upon separation of the phases from the W/O emulsions, the crude is commonly drawn off the top of the desalter and sent to the fractionator tower in crude units or other refinery processes. The water phase may be passed through heat exchanges or the like and ultimately is discharged as effluent.
In addition to the need for effective emulsion breakers in resolving the W/O emulsions in desalters and the like, W/O emulsions are also commonly employed in certain bitumen demulsification processes. The emulsions encountered can be of the oil in water type, wherein the density of the hydrocarbon materials is greater than that of water. In these cases, the hydrocarbon phase can be taken from the bottom of the vessel used for separation.
Emulsions are also formed during the production of crude oil. Water is associated with the geological formation and will be co-produced from the oil well. Also, water or steam may be added to the formation in enhanced oil recovery operations that will contribute water to the produced oil stream. Turbulence applied by choke points in the wellhead or production adds sufficient mechanical force to create an emulsion from the oil/water mixture. This water needs to be separated from the produced oil, as pipeline and other collection or transportation systems have specs on maximum amounts of water that can be associated with the oil. The water can lead to corrosion issues in the pipeline. Emulsion breakers are applied to speed the separation of the oil and water during production. Various types of equipment have been used to effect this separation such as dehydrators or heat treaters.
Emulsions that become difficult to break or resolve as a result of refinery reworks, tankwashes, interfaces and others are often referred to as “slop”. This “slop” cannot be discharged directly due to environmental concerns so that it has therefore become important to efficiently resolve or separate the emulsion constituents into an oleaginous (oil) phase and a combined mud/non-oleaginous (i.e.) water phase. The oil phase may be used as a process fluid for refinery or other processes or recycled for down hole usage. The mud/water phase may be sent to further separation processes to separate the water for discharge or other use and the mud for possible recycling into down hole operations. Additionally, in some cases, the drilling mud actually seeps out of formation into the crude oil that is being extracted to form an undesirable drilling mud emulsion containing crude oil, water, and sometimes clay as components.
Accordingly, there is a need in the art to provide effective demulsifying treatments to resolve or break water and oil emulsions, particularly the crude oil emulsions encountered in desalter apparatuses, water and bitumen emulsions, and drilling mud emulsions. The emulsions may also be encountered in heat treaters, free water knockout apparatus, inclined plate separation apparatus, water separation apparatus, hydrocyclones, and centrifuges.